Effect of hydrothermal pretreatment severity on lignin inhibition in the enzymatic hydrolysis of lignocellulosic biomass

It is frequently seen that enzymatic hydrolysis of carbohydrates in lignocellulosic biomass is inhibited by non-productive adsorption of enzymes on the lignin surface. To compensate partial enzyme adsorption, enzyme dosages have generally remained high and enzymes continue to be a major cost in sugar production from lignocellulosic biomass. The high process cost in biorefineries could partially be overcome by minimizing non-productive binding and thereby promoting the reuse of enzymes. Thermochemical pretreatment is predominant for lignocellulosics to make the cell wall carbohydrates more susceptible to enzyme degradation. Our previous work has shown that pretreatment of lignocellulose alteres the lignin chemistry and enhances enzyme adsorption onto lignin. The present study further examines the effects of thermochemical pretreatment on lignin chemistry and enzyme adsorption. Spruce and wheat straw were pretreated under hydrothermal conditions from 180 to 220 °C in the presence or absence of a dilute acid catalyst (H₂SO₄). Lignins under different pretreatment severities were isolated and analyzed in order to identify the changes introduced by the pretreatment. This paper will discuss the effect of pretreatment severity on enzymatic hydrolysis and non-productive adsorption of enzymes onto lignin.